A 49-year-old woman is referred because her hs-troponin I has been between 180 and 210 ng/L (99th percentile upper reference limit 16 ng/L) on five occasions over 8 months, always without chest pain. ECG, echocardiogram and coronary CT angiography are normal, and eGFR is 95 mL/min/1.73 m². On the same samples, hs-troponin T is 6 ng/L (99th percentile 14 ng/L) and CK is normal. Re-testing troponin I after treatment with a heterophile blocking reagent gives the same result. After polyethylene glycol (PEG) precipitation, 15% of the troponin I is recovered, against 60-80% for control samples. What is the most likely explanation?

Macrotroponin: troponin I bound to an autoantibody

Troponin released from diseased skeletal muscle

Heterophile antibodies interfering in the assay

Chronic myocardial injury from hidden heart disease

Compared with BNP, NT-proBNP rises more as kidney function declines. The main reason is that NT-proBNP:

Is cleared mainly by the kidneys

Is released by damaged nephrons

In a patient with heart failure treated with sacubitril-valsartan, NT-proBNP is preferred to BNP for monitoring because:

Sacubitril raises BNP but does not raise NT-proBNP

NT-proBNP is unaffected by kidney function

Sacubitril cross-reacts in BNP immunoassays

Valsartan blocks release of BNP from the ventricles

A troponin assay is classed as high-sensitivity when its total CV at the 99th percentile is 10% or less and it also:

Detects troponin above the LoD in at least half of healthy people

Gives undetectable troponin results in all healthy people

Detects troponin within one hour of the onset of chest pain

Measures troponin I and troponin T in the same reaction

A 45-year-old woman taking 10 mg of biotin daily for hair loss has typical chest pain and ST depression. Her hs-troponin T, measured by a streptavidin-biotin sandwich immunoassay, is below the limit of detection at 0 h and 3 h. What is the most appropriate step?

Retest troponin on an assay that does not use biotin capture

Report that myocardial injury has been excluded

Replace troponin with myoglobin and total CK

Retest the same assay after a heterophile-blocking tube

Cardiac biomarkers

15 DOH Abu Dhabi (HAAD) lab licensing practice questions on Cardiac biomarkers, part of Clinical Chemistry. The first 15 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 49-year-old woman is referred because her hs-troponin I has been between 180 and 210 ng/L (99th percentile upper reference limit 16 ng/L) on five occasions over 8 months, always without chest pain. ECG, echocardiogram and coronary CT angiography are normal, and eGFR is 95 mL/min/1.73 m². On the same samples, hs-troponin T is 6 ng/L (99th percentile 14 ng/L) and CK is normal. Re-testing troponin I after treatment with a heterophile blocking reagent gives the same result. After polyethylene glycol (PEG) precipitation, 15% of the troponin I is recovered, against 60-80% for control samples. What is the most likely explanation?
1. ATroponin released from diseased skeletal muscle
2. BHeterophile antibodies interfering in the assay
3. CMacrotroponin: troponin I bound to an autoantibody
4. DChronic myocardial injury from hidden heart disease
Show answerHide answer
Answer: C · Macrotroponin: troponin I bound to an autoantibody
The troponin I is high but stable over months, with no symptoms, normal cardiac imaging and a normal troponin T, which is not the pattern of myocardial injury. PEG precipitates immunoglobulins, so the low recovery shows that most of the measured troponin I is bound to immunoglobulin; this macrotroponin is cleared slowly and builds up in the blood. Heterophile antibody interference is unlikely because the blocking reagent did not change the result. Diseased skeletal muscle can raise troponin T results but not troponin I, and here troponin T and CK are normal. Recognising macrotroponin, by gel filtration if needed, prevents repeated cardiac investigations, and a troponin T assay can be used for this patient in future.
- A: Skeletal muscle disease raises troponin T, not troponin I, and her CK is normal.
- B: The heterophile blocking reagent did not change the result.
- D: Myocardial injury would also raise troponin T, and her heart studies are normal.
Question 2 · Medium
Compared with BNP, NT-proBNP rises more as kidney function declines. The main reason is that NT-proBNP:
1. AIs cleared mainly by the kidneys
2. BIs released by damaged nephrons
3. CIs broken down by neprilysin
4. DIs cleared by receptor binding
Show answerHide answer
Answer: A · Is cleared mainly by the kidneys
NT-proBNP is biologically inactive and is removed from the blood mainly by glomerular filtration, so its concentration rises steeply in chronic kidney disease. BNP is cleared largely by natriuretic peptide clearance receptors and neprilysin, with a smaller renal share. Higher cut-offs, or comparison with the patient's own baseline, are needed in kidney disease. NT-proBNP also rises with age, which is why age-related cut-offs are used.
- B: Natriuretic peptides come from heart muscle, not the kidney.
- C: Neprilysin degrades BNP; NT-proBNP is not a substrate.
- D: Clearance receptors remove BNP, not NT-proBNP.
Question 3 · Medium
In a patient with heart failure treated with sacubitril-valsartan, NT-proBNP is preferred to BNP for monitoring because:
1. ANT-proBNP is unaffected by kidney function
2. BSacubitril raises BNP but does not raise NT-proBNP
3. CSacubitril cross-reacts in BNP immunoassays
4. DValsartan blocks release of BNP from the ventricles
Show answerHide answer
Answer: B · Sacubitril raises BNP but does not raise NT-proBNP
Sacubitril inhibits neprilysin, the enzyme that degrades BNP, so BNP rises as a direct drug effect even when heart failure improves. NT-proBNP is not a neprilysin substrate, so it still reflects cardiac wall stress. During treatment, a falling NT-proBNP indicates a good response. Both peptides are released in equal molar amounts when proBNP is cleaved.
- A: NT-proBNP depends more on kidney clearance than BNP does.
- C: The rise in BNP is a true in vivo effect of neprilysin inhibition, not assay cross-reactivity.
- D: Valsartan blocks angiotensin receptors and does not block natriuretic peptide release.
Question 4 · Medium
A troponin assay is classed as high-sensitivity when its total CV at the 99th percentile is 10% or less and it also:
1. ADetects troponin above the LoD in at least half of healthy people
2. BGives undetectable troponin results in all healthy people
3. CDetects troponin within one hour of the onset of chest pain
4. DMeasures troponin I and troponin T in the same reaction
Show answerHide answer
Answer: A · Detects troponin above the LoD in at least half of healthy people
IFCC criteria define a high-sensitivity troponin assay by two features: a CV of 10% or less at the 99th percentile, and measurable results above the limit of detection (LoD) in at least 50% of healthy men and women. Measuring low concentrations precisely allows small changes between serial samples to be detected. This is what makes rapid 0/1-hour and 0/2-hour protocols possible. Results are reported in ng/L as whole numbers.
- B: It is older, less sensitive assays that gave undetectable results in healthy people.
- C: Release kinetics, not assay sensitivity, set when troponin first rises after injury.
- D: Each assay measures either troponin I or troponin T, not both.
Question 5 · Hard
A 45-year-old woman taking 10 mg of biotin daily for hair loss has typical chest pain and ST depression. Her hs-troponin T, measured by a streptavidin-biotin sandwich immunoassay, is below the limit of detection at 0 h and 3 h. What is the most appropriate step?
1. AReport that myocardial injury has been excluded
2. BReplace troponin with myoglobin and total CK
3. CRetest the same assay after a heterophile-blocking tube
4. DRetest troponin on an assay that does not use biotin capture
Show answerHide answer
Answer: D · Retest troponin on an assay that does not use biotin capture
In streptavidin-biotin sandwich assays, high biotin in the sample saturates the streptavidin on the solid phase, so the labeled sandwich is not captured and the result is falsely low. Supplements of 5-10 mg a day can reach interfering concentrations for several hours after a dose. With a convincing clinical picture, troponin should be measured by an unaffected method, or after a documented biotin washout. Competitive assays using the same capture system show the opposite error, a falsely high result.
- A: A falsely low result cannot exclude injury in a patient with ischemic features.
- B: Myoglobin and total CK are less specific and are not substitutes for troponin.
- C: Heterophile blockers do not remove biotin, which acts on the capture step.
Question 6 · Hard
A 70-year-old man on hemodialysis attends a routine clinic with no symptoms. Hs-troponin T is 42 ng/L, and 44 ng/L 3 hours later (99th percentile 14 ng/L; a significant change for this assay is 20% or more). How should these results be interpreted?
1. AAcute myocardial infarction, needing urgent treatment
2. BChronic myocardial injury, without an acute change
3. CLaboratory error, since troponin is never raised in CKD
4. DNormal result once corrected for kidney function
Answer and explanation in LearnFree account
Question 7 · Medium
A man comes to the emergency department 5 days after an episode of severe chest pain. If he had a myocardial infarction, which marker is most likely still raised?
1. ATotal CK
2. BMyoglobin
3. CCK-MB
4. DCardiac troponin
Answer and explanation in LearnFree account
Question 8 · Hard
A 55-year-old man with long-standing inflammatory myositis has no chest pain, a normal ECG and an eGFR of 95 mL/min/1.73 m2. Hs-troponin T is 65 ng/L (99th percentile 14 ng/L) and stable over 6 hours; hs-troponin I is 3 ng/L (99th percentile 26 ng/L); CK is 2,400 U/L (reference < 200 U/L). The best explanation is:
1. ATroponin T released by diseased skeletal muscle
2. BSilent myocardial infarction seen only with troponin T
3. CBiotin interference raising troponin T
4. DChronic kidney disease raising troponin T
Answer and explanation in LearnFree account
Question 9 · Hard
A 30-year-old man has muscle pain after a marathon. Total CK is 4,000 U/L (reference < 200 U/L) and CK-MB mass is 40 µg/L (reference < 5 µg/L). The laboratory uses a relative index (CK-MB mass ÷ total CK x 100) above 2.5% to suggest a cardiac source. What is the relative index, and what does it suggest?
1. A1.0%: consistent with a skeletal muscle source
2. B1.0%: cardiac, because CK-MB mass is above 5 µg/L
3. C0.01%: CK-MB is not truly raised
4. D10%: consistent with a cardiac source
Answer and explanation in LearnFree account
Question 10 · Easy
In the Fourth Universal Definition of Myocardial Infarction, a cardiac troponin value is called raised when it is above the:
1. A97.5th percentile upper reference limit
2. B99th percentile upper reference limit
3. CMean plus two standard deviations
4. D95th percentile of a healthy population
Answer and explanation in LearnFree account
Question 11 · Medium
In obese patients with heart failure, BNP and NT-proBNP results tend to be:
1. AHigher than expected for the severity
2. BFalsely raised by lipemia
3. CUnaffected by body weight
4. DLower than expected for the severity
Answer and explanation in LearnFree account
Question 12 · Hard
A hospital's validated 0/1-hour protocol for its hs-troponin T assay is: rule out if 0 h is below 12 ng/L and the 1-hour change is below 3 ng/L; rule in if 0 h is at least 52 ng/L or the 1-hour change is at least 5 ng/L; observe all others. A patient with chest pain for 4 hours has 18 ng/L at 0 h and 25 ng/L at 1 h. Which group applies?
1. ARule in, because the 1-hour change is 7 ng/L
2. BObserve, because the 1-hour value is below 52 ng/L
3. CObserve, because the 0-hour value is between 12 and 52 ng/L
4. DRule out, because the 0-hour value is under 52 ng/L
Answer and explanation in LearnFree account
Question 13 · Medium
A 64-year-old man is in the coronary care unit after an acute myocardial infarction. His serial hs-troponin I and CK-MB results are plotted. What best explains the change after day 3?
Figure: MedExams
1. AHeterophile antibody interference
2. BExpected late troponin peak
3. CReinfarction
4. DSkeletal muscle injury
Answer and explanation in LearnFree account
Question 14 · Medium
The curves show the typical release of four markers after a myocardial infarction, each as a multiple of its upper reference limit. The curve that represents CK-MB is:
Figure: MedExams
1. ACurve C
2. BCurve B
3. CCurve A
4. DCurve D
Answer and explanation in LearnFree account
Question 15 · Easy
What are BNP and NT-proBNP mainly used for?
1. ADiagnosing acute myocardial infarction
2. BScreening for thyroid disease
3. CDiagnosing and ruling out heart failure
4. DAssessing liver synthetic function
Answer and explanation in LearnFree account

Cardiac biomarkers

Compared with BNP, NT-proBNP rises more as kidney function declines. The main reason is that NT-proBNP:

In a patient with heart failure treated with sacubitril-valsartan, NT-proBNP is preferred to BNP for monitoring because:

A troponin assay is classed as high-sensitivity when its total CV at the 99th percentile is 10% or less and it also:

A 45-year-old woman taking 10 mg of biotin daily for hair loss has typical chest pain and ST depression. Her hs-troponin T, measured by a streptavidin-biotin sandwich immunoassay, is below the limit of detection at 0 h and 3 h. What is the most appropriate step?

A 70-year-old man on hemodialysis attends a routine clinic with no symptoms. Hs-troponin T is 42 ng/L, and 44 ng/L 3 hours later (99th percentile 14 ng/L; a significant change for this assay is 20% or more). How should these results be interpreted?

A man comes to the emergency department 5 days after an episode of severe chest pain. If he had a myocardial infarction, which marker is most likely still raised?

In the Fourth Universal Definition of Myocardial Infarction, a cardiac troponin value is called raised when it is above the:

In obese patients with heart failure, BNP and NT-proBNP results tend to be:

A 64-year-old man is in the coronary care unit after an acute myocardial infarction. His serial hs-troponin I and CK-MB results are plotted. What best explains the change after day 3?

The curves show the typical release of four markers after a myocardial infarction, each as a multiple of its upper reference limit. The curve that represents CK-MB is:

What are BNP and NT-proBNP mainly used for?